1. Field of the Invention
The present invention relates to a rotational driving apparatus and a camera using the rotational driving apparatus, and more particularly to a rotational driving apparatus to be used as a rotational driving source for a lens device in which a lens is moved forward and backward along the optical axis by a cam mechanism, and a camera using the rotational driving apparatus.
2. Description of the Related Art
In the case where rotation of a motor is to be decelerated at once, for example, a worm gear is usually used. A worm gear consists of a worm and a worm wheel. In the case where rotation of a motor is to be decelerated at once, a worm is previously attached to an output shaft of the motor, and rotation of the motor is transmitted to a worm wheel which meshes with the worm, thereby immediately decelerating the rotation.
Usually, a worm is attached to an output shaft of the motor by press fitting. There is a possibility that the press fitting is loosened as a result of a long term use and the worm moves on the output shaft to slip off from the output shaft.
In JP-A-2001-309610, therefore, the tip end of a worm which is press fitted to an output shaft of a motor is pressed by a pressing member such as a spring, thereby preventing the worm from slipping off.
In the worm supporting structure disclosed in JP-A-2001-309610, however, the pressing force which is applied to the worm by the pressing member cannot be adjusted, and hence there is a drawback that, when the components have a dimensional error, an adequate pressing force cannot be applied to the worm. As a result, the structure has drawbacks that an excessive pressing force is applied to the worm to produce a friction loss, and that, when the pressing force is insufficient, backlash occurs in the worm.